FRANKFURT, March 12 (Reuters) - Fresh talks between Uniper and top shareholder Fortum include a water-testing licence the German firm owns in Russia, its finance chief said on Tuesday, seen as a major hurdle to a complete takeover.

Christopher Delbrueck was speaking after Uniper reported a 22 percent drop in 2018 operating profit and said it could fall by more than a third this year, partly due to a suspension of capacity payments in Britain.

Relations between Uniper and state-owned Finnish group Fortum have been strained since Fortum failed to fully acquire Uniper in 2017. Fortum later bought a 47 percent stake from Uniper’s former parent E.ON and has since raised its stake to 49.99 percent.

For now that is the maximum it can own after Russian authorities prevented a full takeover, saying a critical water-testing licence owned by Uniper’s Russian unit Unipro must not be majority-owned by a foreign state-owned entity.

Last month, Fortum and Uniper said they would make a new effort to explore areas of cooperation and that there would be no taboos in discussions, a comment that raised hopes for a full takeover.

“Therefore, by nature, everything which also relates to the Russian permit is a principle matter of discussion,” Delbrueck told analysts. “Whether and how decisions will be taken really depends on the whole total package and that is a fairly complex situation.”

EQUALS

Delbrueck, who will step down from his post in August, said that a working group, in which Uniper is represented by Chief Operating Officer Eckhardt Ruemmler and Chief Commercial Officer Keith Martin, had started talks.

Discussions will draw into late summer before producing any results, Delbrueck said.

A spokeswoman for Fortum said that Chief Executive Pekka Lundmark was leading negotiations for the Finnish group, adding both groups have met several times by now. Activist fund Elliott also owns a 17.84 percent stake in Uniper.

Uniper has been opposed to a takeover from the outset, arguing that both companies are not a good strategic fit and that Uniper would be better placed to develop its business independently.

Earlier, Uniper said operating profit fell by more than a fifth in 2018 to 865 million euros ($973.73 million).

The group said it still plans to propose a dividend payment of 390 million euros ($440 million) for 2019, an increase of 18.5 percent on the 329 million, or 0.90 euros per share, it has proposed for 2018. ($1 = 0.8868 euros) (Additional reporting by Anne Kauranen in Helsinki; Editing by Tassilo Hummel/Rashmi Aich and Emelia Sithole-Matarise)